Abstract:

Process for the production of wood-based materials containing wood parts,
comprising the steps a) bringing wood parts into contact with a1)
alkaline binder and a2) thiacloprid and b) pressing a bed of wood parts,
containing wood parts treated according to step a), under pressure at a
temperature of the press contact surfaces of 126° C. to
240° C.

Claims:

1. Process for the production of wood-based materials containing wood
parts, comprising the stepsa) bringing wood parts into contact witha1)
alkaline binder anda2) thiacloprid andb) pressing a bed of wood parts,
containing wood parts treated according to step a), under pressure at a
temperature of the press contact surfaces of 126.degree. C. to
240.degree. C.

3. Process according to claim 1, wherein the wood parts used in step a)
arewood veneer layers, preferably having a thickness of 0.5 to 5 mm and a
length of 50 to 400 cmwood chips, having a width of 10 to 15 mm and a
thickness of 0.6 to 0.8 mm and a length of 5 to 20 cmwood chips having a
length of 0.4 to 15 mmfibres having a length of 0.4 to 6 mm

4. Process according to claim 1, wherein the alkaline binder is a
phenol-formaldehyde and/or phenol-urea-formaldehyde binder.

5. Process according to claim 1, wherein the following ingredients are
used85-97% by weight of wood parts2-10% by weight of alkaline
binders0.0002-0.02% by weight of thiacloprid0.4-2% by weight of water
repellent, based in each case on the finished wood-based material.

6. Process according to claim 1, wherein step b) is effected at a pressure
of 100 to 500 N/cm.sup.2.

Description:

[0001]The invention relates to a process for the production of wood-based
materials, the use of thiacloprid for protecting wood-based materials
from insects, and corresponding wood-based materials per se.

[0002]All preservatives which are also suitable for protecting solid wood
are in principle suitable for protecting wood-based materials. The
application of the preservatives can be effected by a pre-manufacture
treatment, in-process treatment or post-manufacture treatment.

[0003]In the treatment by pre-manufacture treatment and by in-process
treatment, temperatures up to 200° C. in the presence of alkaline
substances (e.g. pH 11-13 in the case of phenolic glues) can occur. These
process conditions affect the preservative and may cause degradation of
the preservative. In an alkali medium, many insecticides are readily
degraded, in particular at elevated temperatures.

[0004]In the search for alternative insecticides which represent high
efficiency in combination with an acceptable toxic profile, thiacloprid
may be mentioned. However, the property profile of the thiacloprid
prevents the in-process or the pre-manufacture treatment under alkaline
conditions.

[0005]Testing of these properties showed that, for example, thiacloprid
was completely degraded at 75° C. after only 15 min in an NaOH
solution having a pH of 13.7 (cf. Example 1).

[0006]For a similar class of systemic insecticides, namely imidacloprid,
the use is described in WO98/18328 for pre-manufacture or in-process
applications, but only from moderate temperatures of the contact surfaces
of the press up to 125° C. (cf. Examples).

[0007]Particularly for the production of the so-called oriented strand
boards (OSB), a class of wood-based materials, these conditions are
however not sufficient. Alternative routes for protecting wood-based
materials from attack and/or degradation by insects were sought, which
routes are also suitable for such drastic conditions.

[0008]Thus, for example during pressing of the chip mats to give the OSBs,
a temperature of up to 200° C. occurs on the contact surface with
the press tool, which temperature, for example is not absorbed by the
outer boards of a plywood but acts directly on the active substance.
Other examples of WO98/18328 describe the use of imidacloprid, for
example, with pH-neutral urea glue (cf. Example 5), which however is not
the source of major stress for the active substance.

[0009]Surprisingly, it was found that highly effective protection from
termites is achieved if wood preservatives according to this invention
are incorporated into wood-based materials which are exposed to very high
temperatures during the production process in the presence of alkaline
glues. The termite resistance was detectable in particular on the
surfaces of the wood-based materials, which were in direct contact with
press tools heated to 190-200° C.

[0010]The invention therefore relates to a process for the production of
wood-based materials containing wood parts, comprising the steps
[0011]a) bringing wood parts into contact with [0012]a1) alkaline binder
and [0013]a2) thiacloprid and [0014]b) pressing a bed of wood parts,
containing wood parts treated according to step a), under pressure at a
temperature of the press contact surfaces of 126° C. to
240° C.

[0017]Different wood parts are suitable as a basis for the production of
wood-based material.

[0018]Wood parts preferably used in step a) of the process are:
[0019]wood veneer layers and/or sections, preferably having a thickness
of 0.5 to 5 mm and a length of 50 to 400 cm [0020]wood chips, in
particular for OSB, preferably having a width of 10 to 15 mm and a
thickness of 0.6 to 0.8 mm and a length of 5 to 20 cm wood chips having a
length of 0.4 to 15 mm [0021]fibres having a length of 0.4 to 6 mm

[0022]Suitable alkaline binders al) are solid or liquid binders,
preferably as aqueous solutions or emulsions, in particular in an aqueous
form having a binder content of 10 to 60% by weight, preferably of 35 to
50% by weight. In particular, those which have a pH of 10-13.5 in the
form of 35 to 50% strength by weight aqueous solution are preferably
used.

[0026]Particularly in the case of OSBs, the beds or mats of wood parts
which are used for pressing contain as a rule a top and a bottom layer
(outer layers) comprising coarser, identically treated wood parts and
enclose at least one middle layer, optionally comprising the finer wood
parts. The middle layers can preferably also contain a non-alkaline
binder or non-phenolic binder, for example a PMDI binder.

[0027]Large-volume drums are preferably used for gluing the wood parts
(for OSB, also referred to as strands).

[0028]The amount of glue and chemicals used varies according to the board
quality, board thickness and method of glue application. In the case of
OSB production, different glue types can be used for the outer and middle
layers. Preferably phenol binders (PF), phenol-urea-formaldehyde binders
(PUF), MUPF (melamine-urea-phenol-formaldehyde) or MUF
(melamine-urea-formaldehyde) binders are used in the outer layer and PMDI
(polymethylene diisocyanate) binder in the middle layer.

[0029]The wood parts are brought into contact with thiacloprid, an
insecticide of the formula

##STR00001##

either separately or together with the alkaline binder. The sequence of
addition is unimportant. Preferably, thiacloprid is applied as an aqueous
solution having a content of 0.2 to 10% by weight, in particular 0.2 to
2% by weight, of active substance to the wood parts. Thiacloprid can also
be mixed with the binder.

[0030]It is also possible to use extenders and fillers for influencing the
adhesive bonding and the processability of the wood-based material, water
repellents, flameproofing agents and fire retardants and dyes, but also
further biocides, such as insecticides and/or fungicides. The application
thereof can be effected in the same way as the application of the
alkaline binder or of the insecticide. Examples of extenders and fillers
are organic meals of cereals and lignocellulosic materials or inorganic
meals. Oils and/or waxes, such as, for example, paraffins in solid form
or as a dispersion, are usual examples of water repellents. Examples of
flameproofing agents and fire retardants are, for example, boric acid,
aluminium hydroxide, ammonium polyphosphates and mono- and diammonium
phosphate.

[0031]Binders other than the alkaline binders can also be used for
bringing the wood parts for optionally concomitantly used middle layers
into contact. Preferably, however, the same preservative (insecticide) is
used.

[0032]The following ingredients are preferably used: [0033]85-97% by
weight of wood parts [0034]2-10% by weight of alkaline binders
[0035]0-10% by weight of non-alkaline binders [0036]0.0002-0.02% by
weight of thiacloprid [0037]0-2% by weight of water repellent, based in
each case on the finished wood-based material.

[0038]After the treatment of the wood parts with additives, as a rule the
bed is scattered to give a mat comprising the wood parts. In the case of
OSB, this is particularly preferred with optimal orientation of the
strands. The strands treated according to step a) pass from scattering
machine hoppers, preferably via application and distribution rolls, to
the scattering heads provided with orienting apparatuses. The orientation
of the outer layer in the production direction is preferably effected
with the aid of disc orientors and the orientation of the middle layer is
preferably effected in the transverse direction by means of
compartmentalized rolls. Both the weight of the scattered mat and the
proportions of outer layer relative to middle layer can be controlled via
weighers. With the use of continuous presses, the mat is preferably
scattered onto a revolving textile belt. From this belt, the mat can then
be transferred to the steel belt of a press. With the use of
multidaylight presses, the mat can be scattered onto revolving screen
sections which are adapted to the heating plate length of the press. By
transverse sawing of the mat in the region of the transitions, it is
possible for these to be introduced individually into the loading
apparatus of the press. Lateral trimming of the mat by a continuously
movable means enables the production of different board widths.

[0039]In step b) of the process according to the invention the binder is
cured in the press under the action of pressure and temperature, and the
mat is pressed to the predetermined thickness. Mainly two press types are
used within OSB production: the multidaylight presses and the continuous
presses.

[0040]The preferred pressures during pressing are as a rule 100 to 500
N/cm2. The preferred temperature is preferably 126 to 210°
C., in particular 150 to 200° C.

[0041]The dwell time in the press is as a rule 4 to 15 seconds per mm of
wood-based material thickness (board thickness).

[0042]The invention furthermore relates to the use of thiacloprid for
protecting wood-based materials containing wood parts from attack and/or
degradation by insects, in particular termites, characterized in that the
wood-based materials contain alkaline binders. Otherwise, the
abovementioned preferred ranges are applicable.

[0044]Surprisingly high stability of the wood-based materials to termites
was found as a result.

EXAMPLES

Example 1

[0045]Investigation of the Thermal Lability of Thiacloprid

[0046]5 g of NaOH were dissolved in 250 ml of distilled water (pH 13.7)
and 100 mg of active substance were added. Stirring was then effected for
15 min at different temperatures. The mixture was extracted twice with
methylene chloride, neutralized and evaporated down. The residue was
weighed and was analysed by NMR, GC, GC-MS or HPLC.

[0047]Thiacloprid was stable at a temperature of 35° C. and
underwent 100% degradation at a temperature of 75° C.

Example 2

[0048]Pine chips (strands for the production of OSB) whose fine fraction
of <6 mm was removed by means of screening were wetted with
phenol-formaldehyde glue (PF, manufacturer Georgia Pacific; type GP 155 C
42; pH about 11-13) for the outer layers and with polymethylene
diisocyanate glue (PMDI; manufacturer Bayer; type Desmodur 1520 A 20) for
the middle layer. The outer and middle layer chips treated in each case
were then wetted with an aqueous solution containing 0.5% of thiacloprid
and finally in each case with a wax emulsion (Sasolwax Hydrowax 730). The
application was effected in each case using an atomizer (spinning disc
system) in a chip mixer. The amount of alkaline binder was 4.5% of PF (or
2.5% of PMDI) solid resin mass fraction in the finished OSB board. This
corresponds to about 10% mass fraction, based on the chips used, for the
PF glue. The aqueous solution containing thiacloprid was used with 2000
ml/m3 of finished OSB board. At a density of 650 kg/m3, this
corresponds to 0.00153% of thiacloprid, based on the finished OSB board.
The proportion of wax was 0.8% by mass, based on the OSB board.

[0049]The OSB wood composites produced were produced from 60% of PF
glue-coated chips as outer layers and 40% of PMDI glue-coated chips as
the middle layer in a press at 500 N/cm2 and with press plate
temperatures of 190-200° C.

[0050]The finished boards had a density between 650 and 680 kg/m3 and
a thickness of 11-12 mm. The heating time factor was 12 s/mm (i.e. after
application of the pressure, the board surfaces were in direct contact
with the heated press plates for about 12 s/mm×12 mm=244 seconds).
Samples of the OSB boards were subjected to tests analogous to EN 117
(termite resistance in compulsory test with the termite species
Reticulitermes santonensis). The evaluation was effected by inspection of
the surfaces after 8 weeks. No measurable traces of feeding were found on
the test specimens while composite OSB materials without the addition of
thiacloprid had pronounced traces of attack.